Best to use dried leaf, as not drying the plant material will cause the oil to go rancid.
Just follow a traditional herbal medicine oil extraction process. Lots of books out there.
If you are using seeds, lightly roast them first, grind and then cover with oil.

I'm a retired chiropractor, but still treat the occasional patient.
Recently have been using a isoproponol Datura leaf extract on stubborn joints,
with full consent of my patient/friends, really helps to loosen joints before an adjustment.
Really, in all my years of practice, I've never found anything as good. I think I've mentioned before,
that topical tropanes are the most widely used musculoskeletal pain medicines on this planet,
that's saying something! Just DON'T overdo it!!

I've got some seed that's a few years old now, but should be OK.
A decoction is the traditional way, I've found this excellent, with a bit of honey.
The herb can be boiled several times before it loses potency.
Effects are really strong, as a sedative. More deep body relaxation, with very clear mental functioning.
A bit like cannabis without all the racing mental bullshit!

Thanks waterboy 2.0.
Got some seed and a commercial grower will have 15 plants for me during Spring.
There is no commercial industry anymore, at least not in East Gippsland. Undoubtedly, there are superior phenotypes,
they were bred by allowing cross pollination of pot grown plants over a 7 year period, I recall.
Most importantly, the whole plant is harvested just before seeds are ready to drop. The plant is dried, and then a fluid extract (50%) alcohol used to capture the actives. This method ensures maximum potency regardless of phenotype.
Also sourced some salve, great for skin inflammation, and the dried herb I received,
makes a lovely tea, good for digestion.

I have used tropane containing ointment on myself for control of severe pain.
A TINY (Index finger-tip dab) amount is needed, directly on the painful area.
Beware that approx. 20% people have a delayed response to tropanes, DON"T up-dose if delayed response upon application.
Another 20% are very sensitive to tropanes, never use heroic dose applications!
Topical application results in local anesthesia and CNS pain modulating effects.
Do not apply for more than 3 days in a row, have a break of a few days between.
Tolerance to topical microdosing is generalized thruout the body, except the heart muscle,
do not use if you have any cardiovascular conditions.
Stop if you start losing your memory, have blurred vision, dry mouth.
That said, datura ointment is an excellent topical pain killer, used extensively around the world for such.
https://banefolk.com/

Good point Glaukus,
EO's are great, but do miss the whole plant benefits, especially for baths, e.g eucalyptus oil is not as effective (medicinally) as the whole leaf.
BTW, I've burned incense all my life, always had a solid fuel heater, I used to smoke filter-less rollies and other high tech smoking instruments.
Had a pulmonary perfusion CT scan the other day, mild emphysema in the upper lobes of both lungs was found, an incidental finding for my presentation,
not clinically relevant.
I'm not saying that smoke is safe, but common sense in my case has only resulted in a dry dog's nose, and lots of enjoyment for me!

I used to overdo it, dried my dog's nose. Now I tend to use Japanese incenses for smaller confined spaces (as they were designed for), can even get smokeless Japanese incense. I use Bakhoor and Indian (designed for open temples in India) in more open situations, or burn before entering a space.